The binding of highly purified SV40 T antigen (isolated from SV 80 transformed cells) to single and double strand DNA will be examined with respect to relative affinities and with respect to site specificity. The biochemical basis for the difference between the DNA binding and nonbinding forms of SV40 T antigen will be examined and we shall continue our efforts to develop a system which can critically examine the potential role of T antigen in the initiation of DNA synthesis.